Caption: False-colour scanning electron micrograph (SEM) showing the effect of an antibiotic on the bacterium Staphylococcus aureus. Here, the field of roughly spherical bacteria is scattered with the remains of cocci destroyed by lysis (bursting) Lysis is achieved by the destruction of the outer cell wall and the subsequent release of the intracellular contents into the surrounding medium. S. aureus is a Gram-positive species of bacteria that is the commonest cause of pyogenic (pus-forming) infections in humans. It has evolved a number of variants resistant to antibiotics. Magnification: x12,000 at 6x7cm size, x6,000 at 35mm size.